15. Communities

Question 1

Define community and identify the characteristic associated with communities

Answer 1

all the organisms that live together in a specific place

Question 2

Compare and contrast species richness and diversity

Answer 2

• Species richness : the number of species present
• Species Diversity : number of different types of species present

Question 3

Outline the impact keystone and exotic species have on the diversity of community

Answer 3

Keystone Species
- increase Species Richness
- manipulate the environment in ways to stabilize the community
- affect the composition of populations in a community
- e.g. Starfish eat barnacles, allowing other species to thrive instead of being crowded out by the explosive population of barnacles

Exotic Species
- destabilize the community
- inhabit an ecosystem having no predator to control population size
- e.g. Asian carp deplete the base of the food chain thus upset the survival abilities of many species; heading into the Great Lakes

Question 4

Describe the different interactions among populations

Answer 4

Competition (-/-): when individuals use the same resources
Commensalism (+/0): one species benefits but the other is unaffected
Mutualism (+/+): benefits both
Predation or Parasitism (+/-): when one organism eats or absorbs nutrients from another, increasing the consumer’s fitness but decreasing the victim’s fitness
Herbivory (-/+): a plant or portions of the plant consumed by an animal

Question 5

Effects of symbiosis on evolution

Answer 5

Morphology changes: to improve predator/prey interactions

Defensive Coloration: Cryptic coloration or aposematic
Camouflage: may be seasonal
Mimicry:
- Batesian – harmless species mimics a harmful one
- Müllerian – one learned lesson needed for predator

Question 6

Types of competition

Answer 6

Intraspecific competition
- Within the same species
- can regulate population dynamics (size)
- individuals within a population require the same resources, crowding causes resources to become more limited

Interspecies competition
- Two different species use the same limited resource

Question 7

Define NICHE and resource partitioning

Answer 7

Niche: how a population responds to the distribution of resourcesand competitors
Resource partitioning:
-Fundamental niche
-Realized niche

Question 8

Differentiate between fundamental and realized niche

Answer 8

Fundamental niche: entire niche that a species is capable of using, based on physiological tolerance limits and resource needs
Realized niche: actual set of environmental conditions used; presence or absence of other species in which the species can establish a stable population

Question 9

Explain the competitive exclusion principle of Gauss and how it relates to populations in a community

Answer 9

if two species are competing for a limited resource, the species that uses the resource more efficiently will eventually eliminate the other locally

Question 10

Describe the different competitive interactions among species and how they act as agents of evolution

Answer 10

Species act as agents of natural selection. They place selective pressures on each other.

Question 11

Describe succession and the steps (tolerance, facilitation and inhibition) leading to the various stages

Answer 11

Succession: how community plants evolve, a response to disturbances

1. Tolerance: early successional species are characterized by r-selected species tolerant of harsh conditions
2. Facilitation: early successional species introduce local changes in the habitat. K-selected species replace r-selected species
3. Inhibition: changes in the habitat caused by one species inhibits the growth of the original species

Question 12

Differentiate between primary and secondary succession

Answer 12

Primary succession begins with the formation of soil from parent material while secondary succession has soil already present.

Secondary succession occurs quickly while primary succession is very slow